The invention relates to a safety device for a centrifugal separator having a rotating centrifuge drum for the separation or clarification of liquid mixtures, having a hood disposed on the separator housing and surrounding with clearance the centrifuge drum, having an inlet tube centrally disposed in the hood top for the liquid to be separated or clarified, and having one or more paring disks fastened to the hood top and disposed in the drum top with clearance from the drum for the withdrawal of the separated and clarified liquid phases, the shafts of the paring disks being surrounded by an offtake fastened to the hood top.
Safety devices for such centrifugal separators are known and are intended to prevent the loosening of the fittings or the opening of the hood while the drum is rotating and to permit same only when the drum is at a standstill. When the fittings are loosened or the hood is opened, the paring disks disposed in the drum top may either drop down into the drum or come in contact with the drum so as to be caught by the rotating drum, frequently causing considerable damage to the separator and endangering the personnel.
German Pat. No. 1,101,296 has disclosed a safety device for such a centrifugal separator, in whch a gripping body is disposed in the offtake on the hood of the separator for the fastening of the paring disk shaft, and the gripping body is locked against rotation while the drum is rotating. The locking device consists of a rotatable or displaceable element which by spring force can be displaced to the one end position and can be shifted electrically against the spring force to the other end position. The dependence of the locking action on the rotation of the drum is brought about by providing on a shaft of the separator drive a generator which produces the electrical voltage. This voltage, however, is so low when the drum is turning at low speed that it is not an adequate locking voltage.
According to German Petty Patent No. 6,948,132, another, expensive safety device is proposed for centrifugal separators which involves a standstill detector which keeps the line connections locked until the drum is at an absolute standstill. The standstill detector is based essentially on an inductive probe supplied with high frequency voltage, and a disk disposed on a drive shaft and provided on its circumference with a plurality of notches or projections which when the shaft rotates move past the probe and produce a modulation of the high-frequency voltage. This is used as a locking voltage for the line connections fastened to the hood.
German Pat. No. 2,046,084 discloses a mechanically acting safety device for solid jacket centrifugal separators, in which an element which is displaceable towards the drum and can swing away therefrom and which upon contacting the rotating drum holds the hood or the fittings locked and unlocks them when the drum is standing still. Such safety devices, which are subject to wear against the rotating drum and have a mechanism that is liable to give trouble, are not very desirable.
German Auslegeschrift No. 1,159,861 discloses, in connection with an electrical control system, the disposition of a permanent magnet as a pulse generator on a centrifugal drum, the permanent magnet producing, as it passes an induction coil provided on the separator housing, pulses which are fed through an amplifier to a thyrotron which is extinguished by the occurence of a current pulse and remains extinguished as long as additional current pulses are generated in sufficiently close sequence, thereby preventing the actuation of a relay until no more current pulses occur within a predetermined time span and thereby the locking of the separator cover is released. This apparatus does not release the lock until the separator comes to a stop, but, due to its construction and the use of complex and delicate elements, it is so delicate that its reliability is impaired.